Your company needs to develop an application that needs to have a caching feature. The application cannot afford many cache failures and should be highly available. Which of the following would you choose for this purpose?

Answer options:

A.Use Memcached on an EC2 Instance.
B.Use ElastiCache – Memcached.
C.Use ElastiCache – Redis with Cluster-Mode Enabled.
D.Use Redis on an EC2 Instance.

Answer – C
Cluster Mode comes with the primary benefit of horizontal scaling up and down of your Redis cluster, with almost zero impact on the performance of the cluster, as I will demonstrate later.
ElastiCache for Redis with Cluster Mode Enabled works by spreading the cache key space across multiple shards. This means that your data and read/write access to that data is spread across multiple Redis nodes. By spreading the load over a greater number of nodes, we can both enhance availability and reduce bottlenecks during periods of peak demand, while providing more memory space than a single node could offer. 
Options A and D are incorrect since using a single EC2 Instance would be a single point of failure, not suitable for high availability.
Option B is incorrect since Redis would be better for high availability.
For more information on Redis ElastiCache, please refer to the below URL-
https://docs.aws.amazon.com/AmazonElastiCache/latest/red-ug/WhatIs.html
https://aws.amazon.com/blogs/database/work-with-cluster-mode-on-amazon-elasticache-for-redis/
https://docs.aws.amazon.com/AmazonElastiCache/latest/red-ug/Replication.Redis-RedisCluster.html